The following description provides a summary of information relevant to the present invention. It is not an admission that any of the information provided herein is prior art to the presently claimed invention, nor that any of the publications specifically or implicitly referenced are prior art to the invention.
There has been much work in the field of desalting solutions in macroscopic environments. For example, devices and methods have been developed for removal of charged particles, such as ions, using various forms of chromatography including dialysis across permeable membranes, ion exchange resins, size exclusion resins, and electrodialysis and the like. Typically, these macroscale devices and methods have involved the use of passive removal or exchange of materials by diffusion. These systems require, generally, large volumes of fluids to accomplish the desired ion removal or exchange and achieve the desired ionic strength.
For example, desalting using permeable membranes generally involves use of dialysis tubing having a pore size cut-off that allows various sized materials to pass through the membrane. Such processes might also use a planar membrane whereby a solution to be desalted is passed next to said membrane and ions are exchanged by diffusion. In such systems, the solution is re-circulated for an extended period of time until the ionic strength of the solution is reduced.
In another example, ion exchange resins are typically employed to desalt a solution wherein the solution is passed directly over the exchange resin, such as in a column. Like dialysis, this requires copious amounts of solution volume. Additionally, such a means of desalting presents very large surface area over which a sample, with its target materials, must pass thereby allowing valuable target materials to be lost from the sample by nonspecific binding. Size exclusion resins are used in a similar fashion and present the same types of problems.
In still another example, electrodialysis has been used as applied to desalting copious volumes of water. Specifically, such systems have been used successfully to desalinate sea water wherein charged permselective membranes trap ions with like charge behind similarly charged membranes in a direct current field. (Spiegler, Salt Water Purification, 2.sup.nd ed., Plenum Press, New Your, 1977). Systems such as this that use electronic potential have additional drawbacks in that with increasing time of electrolysis, there is an increasing drop in voltage potential across the permselective membrane due to the buildup of charge across the membrane and this causes decrease in desalinization efficiency. This efficiency problem has been addressed by employing ion exchange resins to sequester the ions once they have been transported across the membrane thereby reducing the local ion concentration. (see U.S. Pat. Nos. 5,316,637, 4,632,745, 5,593,563, and 5,026,465)
Major drawbacks to each of the above methods include the rate at which desalting can occur as well as a limitation of the degree to which desalting can occur. Generally, in such systems, desalting cannot be carried out in an economical fashion to the levels necessary for applicability to micro-volume scales, especially those systems which require use of electronic potentials applied to the micro-volume to induce transport of molecules within the volumes from one point to another. With respect to the current invention, such systems comprise electronically addressable microarrays used in the amplification, isolation, and identification of nucleic acids, proteins, and cells.
Given that there is still a need in the arts for devices and methods capable of efficiently and quickly desalting small volume samples used in connection with electronically addressable microarrays, we have solved such problems by providing a device and method capable of desalting a low volume sample generally in less than 15 minutes, usually in less than 5 minutes, and preferably in less than 3 minutes, to a level of ionic strength, generally less than 100 uS/cm, and preferably less than 50 uS/cm, wherein said sample can be applied to an electronically addressable microarray and analyzed.